1. Field of the Invention
Exemplary aspects of the present invention generally relate to an image forming apparatus, such as a copier, a facsimile machine, a printer, or a multi-functional system including at least two of these functions thereof, and more particularly, to a sheet feeding device employed in an image forming apparatus.
2. Description of the Background Art
An image forming apparatus such as a copier, a facsimile machine, a printer, or a multi-functional system including at least two of these functions also includes a sheet feeding device that stores multiple recording media sheets and feeds the recording media sheets one sheet at a time from the top. The sheet feeding device is generally equipped with a sheet feed tray or a sheet feed cassette in which the recording media sheets are stacked, such that a front portion of the sheet stack is placed on a bottom plate that pushes the sheet bundle upward by rotating about a shaft. The recording media sheets thus raised are then fed onward one sheet at a time from the top of the stack.
In such a sheet feeding device that stacks multiple recording media sheets, as the front portion of the sheet stack is raised, an angle of rotation of the bottom plate from the fulcrum thereof increases, thereby increasing the moving distance of a leading edge portion of the bottom plate in the vertical direction. The system is configured so that the rise of the bottom plate is restrained by the weight of the stack of sheets in the tray or cassette. However, when the number of recording media sheets stacked in the tray or cassette decreases that pressure also decreases, and thus the bottom plate rises still more.
As a result, a distance between the leading edge portion of the bottom plate and an end plate that pushes the trailing edge of the recording media sheets in a sheet feed direction increases, in contrast to a case in which there are multiple recording media sheets on the bottom plate, thus pushing down on the bottom plate. This increase in distance causes the leading edge of the recording medium in the sheet feed direction to retract, preventing a sheet feed roller from contacting the recording medium and thus failing to feed the sheet onward.
To counteract such a difficulty, the end plate is employed so that, regardless of the number of recording media sheets in the tray or cassette, the recording media sheets are pushed to the front of the tray or cassette in the sheet feed direction, thereby aligning the leading edges of the recording media sheets and enabling the sheet feed roller to contact the sheets for reliable sheet feeding operation.
When multiple recording media sheets are stacked on the bottom plate and thus the retraction of the recording media sheet at the leading edge of the bottom plate is insignificant, the end plate does not need to push the trailing edge of the recording media sheets stacked in the sheet feed tray or cassette in the sheet feed direction. However, despite this fact, in related-art approaches the end plate is designed to always push the trailing edge of the recording media sheets in the sheet feed direction regardless of the number of recording media sheets.
With this configuration, when multiple recording media sheets are stacked on the bottom plate, an angle between the bottom plate and a front wall of the sheet feed tray or cassette which the leading edge of the recording media sheets abuts is substantially perpendicular, compared to a case in which the number of stacked recording media sheets is low. As a result, due to the pressure of the end plate, the recording medium is sandwiched and squeezed between the end plate and the front wall at the leading edge side of the bottom plate. Consequently, in such a state, the resilience of the recording media sheets reduces the pressure of bottom plate pressing the sheet feed roller for feeding the recording media sheet, causing a problem in sheet feeding operation.